Total-radiation pyrometer



July 9, 1957 r-i.l M, wORMsx-:R

TOTAL-RADIATION PYROMETER 2 Sheets-Sheet l Original F'iled June 30, 1951[man Wam/55,9 l /M #Law July 9, 1957 E. M. woRMsER TOTAL-RADIATIONPYROMETER 2 Sheets-Sheet 2 Original Filed June 30. 1951 FIG.

3 rwentor ERIC M WOR/V557? 11g w Gttornegs btates llTAL-RADATN PYRMETEREric M. Wormser, New York, N. Y., assignor to Servo Corporation ofAmerica, New Hyde Park, N. Y., a corporation of New York @riginalapplication .lune 30, 11.951, Serial No. 234,433, now Patent No.2,761,072, dated August 23, 1.955. Divided and this application duly 18,11956, Serial No. 60%,645

8 Claims. (Cl. 25d-833) lt is also an object to provide heat-radiationmeasuring means employing improved visual-sighting optics.

A further object is to provide improved means for calibrating aradiation pyrorneter. f

lt is a general object to meet the above objects with a compact andeasily handled assembly that is simple to use and relatively unaffectedby constant abuse.

Other objects and various further features of the invention will bepointed out or will occur to those skilled in the art from a reading ofthe following specification in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preferred forms of the invention:

Fig. l is a vertical sectional view along the axis of a portableradiation pyrometer incorporating features of the invention;

Fig. 2 is a left-end view of the pyrometer of Fig. l;

Fig. 3 is an enlarged sectional View of a part of the pyrometer of Fig.l, as taken in the plane 3 3 of Fig. 1;

Fig. 4 is a simplified block diagram, schematically il lustratingelectric components which may be utilized in conjunction with opticalcomponents of Fig. 1;

Fig. 5 is an optical diagram, schematically illustrating an alternativeoptical arrangement;

Fig. 6 is a front three-quarter perspective view of a portable pyrometergenerally similar to that of Fig. l but incorporating slightmodifications; and

Fig. 7 is an optical diagram schematically illustrating a still furtherarrangement.

Briefly stated, my invention contemplates novel optical combinations andarrangements for use in radiation-responsive measurements in and nearthe visible spectrum, as for example in the so-called far-infraredregion, out to say 25 microns. Such combinations may utilizevisualsighting optics at least partially in common with, or on a commonaxis with, the optics for focussing a distant radiation source upon theradiation-responsive means, whereby parallax problems are avoided. Meansmay be incorporated in, or employed in conjunction with, theradiationresponsive means for effectively chopping the radiationimpinging on the radiation-responsive means, whereby the latter mayrespond quantitatively with respect to a given level. For applicationsdemanding relative accuracy, I have provided means for automaticallybasing the response on a carefully regulated reference source; and, foreven greater accuracy, I disclose means whereby the instrumentrespons1vity of lthe radiation-responsive arent means may be checked andcalibrated as frequently as desired.

Referring to Figs. l to 4 of the drawings, my invention is shown inapplication to a portable radiation pyrometer in which the optics may besubstantially contained in a cylindrical body or housing lil. It is afeature of the embodiment of Figs. l to 3 that visual-sighting opticsincluding an eyepiece 1.1 are lined on an axis common with the axis ofthe collecting optics for the radiation-responsive means. Theradiation-responsive means may comprise a heat-sensitive cell 12contained in a suitable housing 13 and mounted upon a standard 14extending radially into the housing lll. In the form shown, microphonicsin the heat-responsive means l2 and lits associated amplifying means arematerially reduced by assembling the housing l, the standard 14, andpreamplier means 15 together as a unit; this subassembly may be mountedand adjusted as a unit on and within the body or housing 10. A1ongitudinal slot 16 at the front end of the housing 10 may permitslidable insertion of this heat-responsive assembly in clearance withthe standard 14.

The collecting optics may comprise a parabolic mirror i7 mounted at theback end of the body ll). In the form shown, the mirror 17 is carried bya sleeve 18 slidable longitudinally in a counterbore 19 in the housing10, for focusing purposes. The focusing means shown includes a linurledring 20 with a shank 2l threaded into a baci-1 plate 22 forming part ofthe pyrometer housing 10. The mirror assembly l718 includes a back plate23 keyed, as at 24, against rotation with respect to the housing lll. Ashoulder engagement at 25 between the threaded shank 21 and the mirrorbacking plate 23 provides a means whereby longitudinal adjustmenteffected by the knurled ring Ztl may be directly translated to themirror 17 for focusing purposes. The two rays 2d in Fig. 1 illustrateradiation from a distant source (not shown) focused upon theheat-responsive means l2.

In the form of Figs. l and 2, l employ a small fixed mirror 27 tointercept a part of the radiation which would otherwise be focused uponthe heat-responsive means 12 and to reliect this part of the radiationinto the visualsighting optics. Thus, whenever the mirror 17 isadjusted, as for purposes of focusing on the heat-responsive means l2,the radiation employed for visual sighting will also be focused at animaginary location 2S., spaced conjugate to the plate of theheat-responsive means l2 with respect to the mirror surface 27. Rays,such as the rays 29, intercepted by mirror 27, will thus cross over atthe point 28, and the lenses 3@ of the visual-sighting optics may be setfor focus on this point 2S. A cross-hair reticule 4t) at a ray crossoverin the sighting optics 1l may assist in alignment of the device on agiven source to be observed. lt will be appreciated that, once adjusted,both the visualsighting optics and the collecting optics will always befocused at the same collecting distance. Whenever the knurled ring 2liis rotated to focus for another collecting distance, both the sightingoptics and the cell will maintain focusing alignment.

The heat-responsive means l2 is preferably rugged and may be one ofseveral types; l prefer to use so-called thermistor means in the cell1?., and in Fig. 4 l illustrate the employment of two thermistor stripsStZ-31. The strip 12 responds to radiation collected and focused by theoptical head 32, which may be that shown and described in Figs. l and 2;but the strip 3l is not exposed to radiation and acts as a compensatorfor ambient conditions. D.C. drift and other difficulties may be avoidedby deliberately effectively chopping the radiation focussed upon theradiation-responsive strip l2.. This may be accomplished electrically byappropriate modulations in the circuit including the strip 12, or, as inthe form shown,

a mechanical chopping disc 33 may be mounted for rotation so as tointerrupt the impingement of radiation upon the strip i2. In the formshown, a small electric motor 34 mounted externally of the housing 10continuously drives the chopping7 disc 33 by belt-and-pulley means35-36-37. A standard 38 may properly position the shaft upon which thechopping disc 33 and its drive pulley 37 are mounted. In Fig. 4, thedotted square wave 32 schematically represents interrupted radiationpassed by the optical head 32 to the exposed thermistor strip 12.

In the form shown, the radiation-responsive thermistor 12 and thecompensating thermistor 31 are mounted in conjugate arms of a bridgecircuit. Power supply 42 may energize the bridge, and the bridge outputmay be fed through signal-attenuator means 43 to preamplifier 15; theattenuating means 43 may be included in the preamplifier package 15. Thepreamplied signal may be fed by a cable (not shown) to a narrow-bandamplifier 44 in order to eliminate undesired modulation products, andrectirying means 45 and power-amplifier and attenuator means 46 mayshape the envelope of heat-responsive signal appropriately for visualdisplay on a meter 47 and for recording on a conventional recorder 48.

In Fig. 5, I illustrate an alternative optical arrangement providing amore exact basis for quantitative heat measurement, with relativelylittle additional complexity. The arrangement of Fig. may also becharacterized by coincidence of the axis of visual sighting with theaxis of the collecting optics for heat-responsive means 50. However, inthe arrangement of Fig. 5, the thermistor or other heat-responsiveelement of the means 50 is alternatively exposed to radiation collectedby the optics and to radiation from a regulated reference source 51,which may be a so-called black body of carefully regulated temperatureand including optics 52 focussed upon the heat-responsive means 50. Thecollecting optics shown in Fig. 5 is of the so-called Cassegrain systememploying a large concave primary mirror 53 and a small convex secondarymirror 54. Rays collected by the mirrors 53-54 may be passed through anopening 55 in the center of the primary mirror 53 and may be focussed ata cross-over point 56, back of the mirror 53; I have shown a reticule 57at the crossover point, for purposes of pin-pointsighting alignment ofthe device (by means of a viewer 58) upon a particular distant source ofradiation to be observed. In order that the heat-responsive means 50 maybe exposed alternately to the reference radiation from the source 5l andto the distant radiation collected by the optics 53-54, I employ achopping disc 59 having a plane mirror surface. Whenever the choppingdisc 59 is in position to blanket radiation from the reference source51, the mirror surface 59 of the chopping disc may be reilecting thedistant-collected radiation upon the heatresponsive means 50; wheneverthe chopping disc 59 is not reflecting such distant-collected energy, itis eiectively open so as to expose the heat-responsive means 50 to thereference source 51. It will be appreciated that by employing theheat-responsive means 50 in conjunction with signal-processing meanslike that of Fig. 4, one may quantitatively record or observe signalsrepresenting the difference between the reference radiation (at 51) andthe distant radiation (as focused by the collecting optics).

In Fig. 6, I show a simple readily portable pyrometer instrument havingmany of the structural features already discussed in connection withFigs. l to 3. In the arrangement of Fig. 6, however, the visual-sightingoptics does not utilize the main collecting mirror (not shown) for theheataresponsive means 60. Such mirror will be understood to beparaboloidal, as in the case of the mirror 17 of Fig. l, and containedwithin the cylindrical housing 61. The heat-responsive means may againbe mounted upon a standard 62 carried by the preamplifier housing 63 andreceived through a slot 64 at the forward end of the cylindrical housing6l. Chopping means 65 for the incident radiation may be driven by anexternally mounted motor 66. Even though the visual-sighting optics maynot use any part `of the collecting optics, parallax diiculties may beavoided by employment of an otfaxis sight including a small periscopealigned with the axis of the collecting optics. In the form shown, thevisual-sighting means employs an eyepiece 67 on a telescope 68, clampedrigidly to the outside of the housing 61; two 45 -mirror elements 69-70connected by a tube 71 provide the necessary oEset for the periscope,the reflecting axis of the entrance mirror 70 being on the axis of thecollecting optlcs.

In Fig. 7, I show a more refined pyrometer incorporating certainfeatures over the arrangement shown in Fig. 5. As in the case of Fig. 5,the collecting optics may be a Cassegrain system, with a concave primarymirror and a convex secondary mirror 76, the focal length of the systembeing relatively long so that the focal point will lie substantially tothe rear of the primary mirror. For precise sighting, a reticule 77 maybe placed at the focal point, and telescopic viewing means 78 may beplaced beyond the focal point. As also in the case of Fig. 5, arotating-mirror chopping disc 79 may permit heat-responsive means 80 tolook alternately at rays projected by the collecting optics `75,--76 andat rays projected by the lens 81 of aA reference source 82. As thusdescribed, the system of Fig. 7 is the exact duplicate of that of Fig.5, and recorded or otherwise observed signals emanating from theheat-responsive means 80 will present eifectively continuous comparisonbetween the distant radiation and the reference radiation.

In spite of the ascertainable relation (utilizing the parts thus fardescribed in Fig. 7) between the distant radiation and the referenceradiation, instrument responsivity remains as an unknown factor. This isparticularly true in particular applications in which a restrictedportion of the spectrum is being examined, for the heat-responsive means80 is likely to have various responsivities'for various wavelengths. Inorder to make the responsivity readily ascertainable when desired, evenwhile Vmaking a measurement, I may provide what I call a Calibratingsource 83 which may, like the black body or reference source 82, be aconstant radiator of ca refully regulated temperature, with opticalmeans 84 for focusing upon the heat-responsive means 80 when desired. Inthe form shown, a pivotally mounted plane mirror 85 is so arrangedasrtobe normally outof the path of rays projected by the collectingoptics 75g- 76. However, when desired, the mirror 85"may be manuallydepressed against a stop 86 so as to hold a reflecting position blankingoff rays from the collecting optics and casting rays from thecalibrating source 83 directly upon the heat-responsive means 80 in acycle of alternation with rays projected from the reference source 82.

In use, the calibration source 83'isregulated at a temperatureof'theorder of magnitude of the temperature to be observed through thecollecting optics, that is, of the order of magnitude of the temperatureof the `dis tant source, andthe reference source 82 is set for somesubstantially different temperature. For example, if the distant sourceto be observed has a temperature of about to 200 C., then thetemperature of theY Calibrating source83 might'be conveniently regulatedat 150'C., while the reference4 source is regulated at about 80 C. Suchregulation may be accomplished within 0.1" C. by means not shown ordescribed herein.

In use, with the manually operable mirror 85 in the raisedposition,'tlie measurable voltage in the heat-re sponsive means 80 willreflect the difference in radiation between the distant source andthereference source 82. This relationship vwill be Acharacterized by aninstrument responsivity which appears'v as a constant' When the mirror85 is depressed, the voltage in the output of heatresponsive means 80will reflect the dilerence in 'radiation between the reference source 82and the calibrating source 83, and an instrument responsivity willappear as a constant in this relationship. The instrument willpresumably have been calibrated initially for a given responsivity,characterizing alternating exposure between the reference source 82 andthe calibrating source 83; thus, in eld use, if a voltage other than theoriginal calibrated voltage is observed when the mirror 85 is depressed,then the observed percentage voltage change under these conditions willbe a measure of the change in responsivity of the instrument, and anappropriate correcting factor will be available for application to thevoltage reading obtained when the mirror 85 is retracted out of the wayof rays from the collecting optics. More highly reiined measurements maybe made in this manner.

It will be seen that I have disclosed relatively simple pyrometerconstructions featuring ruggedness for the accuracy obtainable. Theoptical-sighting arrangements and the relative compactness permit easyhandling and precise focussing and alignment with sources to beobserved, whether at close or distant range. With little additionalcomplexity, means may be provided for more exact quantitativedeterminations, and instrument responsivity may be checked at any time,thus providing an appropriate correction factor whenever an instrumentreading is taken.

While I have described my invention in detail for the preferred formsshown, it will be understood that modiications may be made within thescope of the invention as deiined in the appended claims.

I claim:

l. In a radiation pyrometer, radiation-responsive means andvisual-sighting means having eiective axes inclined with respect to oneanother in a common plane, chopping means including a mirror oriented tobisect the angle between said radiation-responsive means and saidvisual-sighting means, and collecting optics having an axis aligned withone of said means and facing the mirror side of said chopper, wherebysaid chopper may cause said collecting optics to be focused alternatelyupon said radiation-responsive means and through said visualsightingmeans.

2. In a radiation pyrometer, radiation-responsive means, a referencesource of radiation, collecting optics, and choppingV means including arotating mirror, said collecting optics and said radiation-responsivemeans and said reference source being so disposed with respect to saidmirror that for one position of said mirror said radiation-responsivemeans will be responsive to rays from said collecting optics and foranother position of said mirror said radiation-responsive means will beresponsive to rays from said reference source, both said referencesource and said radiation-responsive means being offset from the axis ofsaid collecting optics, whereby not only may the output of saidenergy-responsive means continuously reflect the comparative evaluationof collected and reference energy levels but the collected energy mayalso be intermittently passed along the axis of said collecting opticsbeyond said chopping means in alternation with passage to saidenergy-responsive means, and further energy-responsive means disposed inthe path of said intermittently passed collected energy.

3. A pyrometer according to claim 2, and including visual-sightingoptics having an axis intercepted by said mirror and so aligned thatsaid collecting optics may be utilized for visual sighting during thoseperiods of time in which said radiation-responsive means is exposed toradiation from said reference source.

4. In a radiation pyrometer, radiation-responsive means, collectingoptics for receiving radiation from a distant source, a chopping mirrorincluding a plane surface inclined to the axis of said collectingoptics, a reference source so arranged with respect to saidradiation-responsive means and said mirror that saidradiation-responsive means may be exposed alternately to radiation fromsaid collecting optics and to radiation from said reference source, acalibration source, and movable means for projecting radiation from saidCalibrating source onto said mirror along the axis of said collectingloptics and to the exclusion of radiation projected through saidcollecting optics, whereby in a first position of said movable meanssaid radiation-responsive means may be alternately exposed to radiationfrom said calibration source and to radiation from said referencesource, and whereby for a second position of said movable means saidradiationresponsive means may be alternately exposed to radiation fromsaid radiation source and to radiation projected through said collectingoptics.

5. A pyrometer according to claim 4, in which visualsighting means areprovided with an axis intercepted by said chopping means and orientedwith respect to said chopping means and said collecting optics so as topermit visual sighting through said collecting optics during instants oftime in which said radiation-responsive means is exposed to radiationfrom said reference source and when said movable means is in said secondposition.

6. In a radiation pyrometer, radiation-responsive means, a referencesource of radiation, collecting optics, chopping means including arotating mirror, said radiationresponsive means and said referencesource being disposed in face-to-face opposition on opposite sides ofthe axis of said optics, said chopping mirror being mounted for rotationabout an axis located substantially intermediate the axis of said opticsand the axis of response of said radiation-responsive means to saidreference source, and said mirror being mounted to focus on saidradiation-responsive means from said source in alternation with energycollected by said optics, whereby not only may the output of saidenergy-responsive means continuously relect the comparative evaluationlof collected and reference energy levels but the collected energy mayalso be intermittentlil passed along the axis of said collecting opticsbeyond said chopping means in alternation with passage to saidenergyresponsive means, and further energy-responsive means disposed inthe path of said intermittently passed collected energy.

7. A pyrometer according to claim 6, in which said furtherenergy-responsive means includes optical viewing means.

8. In a radiation pyrometer, collecting optics having an elongated tirstaxis, a at chopper having a mirror surface and mounted for rotation,said mirror surface being inclined substantially 45 degrees from saidaxis, thereby establishing a reflected second axis substantially atdegrees with respect to said first axis; whereby with rota-tion of saidchopper the optical alignment along said second axis is intermittentlyinterrupted between spaced points on opposite sides of said rst axis,and further whereby optical alignment along said first axis isintermittently interrupted between said optics and a third point on theother side of said second axis, two separate energy-responsive elementsat a iirst two of said points, and a reference energy source at theremaining one of said three points.

Marshall et al. Sept. 30, 1952 Luft May 18, 1954

